Use Caution Mixing Chastetree Berries with Pergolide

Eleanor M. Kellon, VMD

Chastetree berries (CTB), aka Chasteberry, aka Vitex agnus-castus, is an herbal remedy I first published about using in horses with Pituitary Pars Intermedia Dysfunction/Cushing’s (PPID) back in 2000. It had been determined that CTB could help normalize prolactin levels by binding to dopamine receptors in the brain. Low dopamine activity is at the root of PPID, so I decided to try it.

The initial trial was an observational study. All horses were correctly diagnosed but follow-up blood work was not standardized. Emphasis was on signs/symptoms. Response was very positive, especially with coat and foot comfort, but even in this short preliminary study I noted it may not be appropriate for advanced cases and, of course, a lot more work needed to be done. There was also concern about how it might interact with pergolide, since both act by binding to dopamine receptors.

Since then, a study out of New Bolton Center, the University of Pennsylvania School of Veterinary Medicine, found no benefit, but used advanced cases and graduated doses of pergolide compared to a set dose of CTB. The Laminitis Trust in the UK studied horses for at least a year on CTB and contradicted the findings of that study. They confirmed obvious benefits with symptomatology, but no consistent effect on hormone levels like adrenocorticotropic hormone (ACTH).

The latest study1 looked at confirmed PPID horses on CTB alone, CTB plus pergolide, or pergolide alone. Horses on both had better resolution of the abnormal PPID coat but horses on CTB alone or CTB + pergolide had much higher ACTH levels than pergolide alone, indicating CTB can likely interfere with the effects of pergolide. The effect was particularly obvious when the seasonal ACTH rise was approaching.

Pergolide is the gold standard treatment for PPID/Cushing’s and can control the abnormal hormone output from the pituitary. CTB has never been documented to do that, and now it appears it may actually interfere with pergolide effects. This is not surprising since it is competing with the drug for binding sites on dopamine receptors but its effect when bound is apparently not as strong.

The bottom line here is that CTB alone is not an adequate treatment for PPID. Symptoms may improve for a while but the abnormal growth in the pituitary goes unchecked and when CTB stops working the process is much more difficult to get under control. I’ve seen that happen.

This new research also shows you must be careful in combining it with pergolide because the CTB may block the drug’s effects.

To learn more, join the ECIR Group, August 13-15, for the 2021 NO Laminitis! Conference, via Zoom, which continues the mission to serve the scientific community, practicing clinicians, and owners by focusing on investigations most likely to quickly, immediately, and significantly benefit the welfare of the horse.

1Bradaric Z, May A, Gehlen H, Use of the chasteberry preparation Corticosal®for the treatment of pituitary pars intermedia dysfunction in horses. Clinic for Horses, Free University of Berlin, and Equine Clinic, Ludwig-Maximilian-University of Munich, Germany.

About ECIR Group Inc.
Started in 1999, the ECIR Group is the largest field-trial database for PPID and EMS in the world and provides the latest research, diagnosis, and treatment information, in addition to dietary recommendations for horses with these conditions. Even universities do not and cannot compile and follow long term as many in-depth case histories of PPID/EMS  horses as the ECIR Group.

In 2013 the Equine Cushing’s and Insulin Resistance Group Inc., an Arizona nonprofit corporation, was approved as a 501(c)3 public charity. Tax deductible contributions and grants support ongoing research, education, and awareness of Equine Cushing’s Disease/PPID and EMS.

THE MISSION of the ECIR Group Inc. is to improve the welfare of equines with metabolic disorders via a unique interface between basic research and real-life clinical experience. Prevention of laminitis is the ultimate goal. The ECIR Group serves the scientific community, practicing clinicians, and owners by focusing on investigations most likely to quickly, immediately, and significantly benefit the welfare of the horse.

Contact:  Nancy Collins
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